The present invention relates to a composite component which includes a thermally stable composite compact joined to a supporting substrate by a high strength braze joint.
Composite compacts manufactured in accordance with U.S. Pat. No. 3,745,623, which comprise a thin table of polycrystalline, cobalt-infiltrated diamond or boron nitride bonded to a thick cemented carbide substrate, are well known in the cutting and drilling arts. Such composite compacts have been widely used in applications having thermal requirements below 700.degree. C. However, difficulty has been experienced in working with such composite compacts at temperatures approaching 700.degree. C., and has been impossible at sustained temperatures above such limit. Cobalt, which is relied upon as a solvent-catalyst in the manufacturing process of converting graphite to diamond, and which is present in the table as the secondary phase, becomes active at approximately 700.degree. C. at atmospheric pressure, and catalyzes the back-conversion of diamond to graphite, thereby causing the table to degrade and lose its capability as an abrasive.
Efforts to adapt composite compacts to use as cutters for rotary drill bits have been hampered by the inherent thermal instability, at temperatures approaching 700.degree. C., of the commercially available cobalt-infiltrated composite compacts. The abrasion resistance and effective life characteristics of such composite compacts have been attractive for such use, but the inability to attach them securely to a drill bit, such that they will be retained in cutting position under the wide range of extremely adverse conditions encountered in drilling hard rock formations, compressive strengths of 20,000 psi and above, has limited their use. For reasons of cost, brazing has been the method of choice for securing a composite compact to a stud or pin to be mounted on a drill crown. However, the strength of a braze joint is directly related to the liquidus of the braze filler metal used, and the high strength braze filler metals have a liquidus greater than the degradation temperature, 700.degree. C., of the polycrystalline table.
A solution to this dilemma was offered by U.S. Pat. No. 4,200,159 in the suggestion of cooling the composite compact while it is soldered at high temperatures, and by U.S. Pat. No. 4,225,322 in the teaching of cooling the polycrystalline table with a heat sink while brazing the thick substrate to a cemented carbide pin or stud with a high liquidus braze filler metal. This technique facilitates production of composite compact cutters for rotary drill bits which utilize the capabilities of the polycrystalline cobalt-infiltrated composite compacts within the limits imposed by the composition of the compacts and by the differential heating of the various parts of the cutters. The use of a solvent-catalyst, such as cobalt, in the prior art composite compacts limits their use to operating temperatures below the degradation temperature of the table. In addition,.the thick cemented carbide substrate, approximately six times the thickness of the table, creates a very significant moment arm through which the working forces applied to the polycrystalline table are transmitted to the braze joint, thus substantially multiplying the effect of such forces on the joint. Furthermore, internal stresses are created within the composite compact during manufacture and within the material of the pin or stud during the brazing process due to the elevated temperatures employed and the differential heating of the substrate and the table.